Our Favorite Toxic Chemical: Nitrate

Today’s post is from guest blogger Melissae Fellet, a science writer based in Santa Cruz, California, and was written for the “Our Favorite Toxic Chemicals” blog carnival hosted by Sciencegeist.

Feeding my vegetable garden so it will feed me

I’m eager to grow some of my own food this summer, so I planted a vegetable garden in pots on my porch. Since my previous gardening experience consists of ignoring my plants, learning some gardening tips was a must.

I hope my plants look this healthy in a few weeks! (Image by flickr user despi88)

Like humans, plants need food, too. Those nutrients come from boosts of nitrogen, phosphorus and potassium-containing fertilizer. But plants need help getting their roots on some nutritious nitrogen when that fertilizer contains kelp, alfalfa, crushed bones, chicken poop and ground feathers, like the organic stuff I put in my garden.

Some of those ingredients contain nitrogen as ammonia, which plants can absorb directly. Proteins are another source of nitrogen. Bacteria in the soil separate proteins into amino acids. Other microbes chomp the nitrogen off the amino acids as ammonia. And super-specialized bacteria eat ammonia and release the nitrogen as nitrate (NO3–). Nitrate is great plant food, too, because it zips through the soil straight to a plant’s roots.

This biological nitrogen transformation is slow, so farmers may feed their plants a nitrate-containing fertilizer to speed growth. That’s a touchy subject in the agricultural areas near my home in California.

About 10 percent of 2500 public water wells tested in the Tulare Valley and Salinas Valley exceed the state limits of 45 mg nitrate per liter of water, according to a report prepared for the state water department last March. The majority of the nitrate in groundwater — about 96% — washes off cropland, the report found.

Nitrate takes time to trickle from a field into the groundwater, so most of that contamination is due to decades of past farming in the area. But if the nutrient pollution trend continues, 80% of the people living in those valleys could be drinking nitrate-laden water by 2050.

Nitrate becomes harmful when our bodies convert it to its chemical cousin, nitrite (NO2–). Nitrite transforms the iron in our blood so that it can no longer carry oxygen. Enough altered iron — 10 percent of the hemoglobin in your blood — causes breathing troubles especially in infants and pregnant women. Higher concentrations can lead to suffocation.

Still, it takes a lot of nitrate to harm a person. According to data from the World Health Organization [PDF], an average three-month old baby boy might have to drink about four liters of water contaminated with nitrate at twice the state limit to induce toxicity. An adult might drink up to 56 liters of the same water at once to get a fatal dose of nitrate.

Excess nitrate can be toxic to the environment, too. The nutrient washes into a Central Coast wetland, feeding microscopic algae until they grow into thick green mats that suffocate ponds and channels.

The UC Davis report says that fertilizer fees and improved groundwater monitoring can help protect drinking water. And policy changes are in the works for one part of the state. In March, the Central Coast Regional Water Control Board passed regulations to reduce nitrate-containing runoff from fields. These rules took three years to negotiate and they are still tangled in a lawsuit from growers.

Even without regulations, farmers can prevent nitrogen pollution by controlling the amount of fertilizer on the fields and feeding plants only what they can absorb. The state report also suggests using nitrate-laden ground water for irrigation. Plants absorb the nitrate from the water, and clean water returns to the aquifer.

Lacking a home nitrate test kit for my garden, I’ll choose organic fertilizer when it comes time to feed my plants again. That should give my plants a slow drip of nitrogen and hopefully prevent a build up of excess nutrients. I feed my plants nitrogen so they’ll be strong and healthy enough to produce food for me.

4 Comments

Great post, Melissae. You reminded me of some ‘case study’ learning we did back in junior year analytical chemistry. We had to figure out how to test nitrate levels in faux well water samples our professor made. The accompanying story involved determining whether parents-to-be moving into a new home would risk their baby acquiring methemoglobinemia, or blue baby syndrome.

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